1. Field of the Invention
The present invention relates generally to the exchange of tape cartridges between tape cartridge libraries and, more particularly, to a system and method for exchanging tape cartridges between automated tape cartridge libraries linked in a library system.
2. Background
Current automated libraries for tape cartridges typically include arrays of multiple storage cells housing the tape cartridges, as well as multiple media drives. Multiple automated robotic devices may be used to move tape cartridges between the various storage cells and media drives within a library. The use of multiple robotic devices raises various problems concerning the distribution of power to such robotic devices. In prior art automated tape cartridge libraries, the movement of the robotic devices is restricted by wire cable connections used for providing such power. Such cabling can prevent the robotic devices from crossing paths, or from continuous movement in one direction around the library without the necessity of ultimately reversing direction.
Such problems can be overcome through the use of power distribution strips or rails. A robotic device traveling over a given route may used fixed conductive strips or rails to supply power to the robotic device, which itself is provided with brushes or wheels that contact the conductive strips or rails in order to conduct power to the robotic device. The integration of such conductive strips or rails into the automated tape cartridge library, in conjunction with brush or wheel contacts provided on the robotic devices, allows for greater freedom of movement of the robotic devices. Moreover, such power distribution systems also provide for modular and extensible power distribution to robotic devices as library configurations change, or as libraries are connected in a modular fashion to form library systems.
In that regard, a number of relatively large automated tape cartridge libraries are known having, for example, between 1000 and 2500 cartridge storage cells. Relatively smaller automated tape cartridge libraries, having for example on the order of 700 cartridge storage cells, are also known. For some users, as storage requirements increase, a smaller automated tape cartridge library may have to be replaced with a larger automated library, often at considerable expense. As a result, there exists a need to allow such smaller automated libraries to be linked together to create larger library systems having, for example, on the order of 1400 cartridge storage cells.
It is known to link the above described larger automated libraries using a variety of pass-through ports and cartridge exchange mechanisms. For example, to ensure maximum access to data stored in the tape cartridges, multiple paths are created between larger automated libraries that employ cam or screw driven cartridge exchange devices. As such devices are located entirely or substantially within a library, little floor space in a data center is compromised by the device. However, the use of multiple paths and interior cartridge exchange devices result in the loss of a large number of cartridge storage cells in each library.
Alternatively, multiple larger automated libraries can be linked linearly to improve access to data. In such configurations, gravity driven cartridge exchange devices are employed between linked libraries. In operation, a tape cartridge is delivered to the cartridge exchange device by a robotic device in one of the libraries. The weight of the cartridge causes the exchange device to rotate and deliver the cartridge to the linked library, where it can be retrieved by another robotic device in that library. This configuration does not result in the loss of large number of storage cells in each library, and only minimally affects floor space. However, only a single cartridge may be passed at a time and, because the exchange device is gravity driven, another path must be provided to exchange cartridges in the opposite direction between the linked libraries. Moreover, more complex host software which sees the linked libraries as a single library, such as Automated Cartridge System Library Server (ACSLS), may be required to control the multiple linked libraries.
The pass-through ports and cartridge exchange mechanisms used in linking the relatively larger automated libraries, however, are not suitable for use in linking the relatively smaller automated libraries in that they do not meet the form factors (e.g., orientation, floor space) required by users needing 1400 cartridge storage cells. Moreover, pass-through ports and cartridge exchange devices that result in the loss of large numbers of cartridge storage cells are unacceptable because such a loss represents a significant percentage of storage space in such smaller libraries. Still further, the development of new tape cartridges having differing weights raises concerns as to the ability of gravity driven cartridge exchange devices to reliably transfer all types of cartridges.
Thus, there exist a need for an improved cartridge exchange mechanism for use in linked automated libraries. Such an improved mechanism would preferably minimize the number of storage cells that may be lost as a result of linking automated libraries, as well as preferably minimize the amount of space required for linking such libraries. Such an improved mechanism would also preferably be capable of reliably transferring a wide variety of cartridge types.